Peter writes:


MikeMl wrote

I personally think this is a DUMB design that causes many more problems
than it prevents.

Overvoltage crowbars are used on switching power supplies which have
instant acting short circuit protection features and whose output
power is limited by the magnetic components anyway.
.....
If one was going to do an overvoltage protector for an aeroplane, the
way to do it is to put something in series with the alternator field
winding (i.e. in series with the existing voltage regulator) which
goes open circuit when the bus voltage reaches say 32V. That will kill
the alternator output very fast.



Err, that field has an inductance of something on the order of
1H. Opening the excitation to it will do what, in the short
term? Crowbarring that field to ground & clearing the 5-10 amp field
breaker sounds like a good idea to me, given the price of avionics in a
aircraft, and the proprensity for people/Murphy to do bad things....

[I've seen car owners yank the battery cable off while the alternator is
going full tilt; "The battery only starts the car; the alternator runs
it..." The result was a 65V+ "load dump" hundreds of ms long into the
car...fried computers, dead stereos, you name it.]

Falsing is a problem with any protective system design. How fast is too
fast? How slow is too slow to save the consumers from overvoltage? It
sounds like the OVP is a shade oversensitive, but I also wonder about the
spikes that trip it. I'd first check grounds: the alternator ground, the
battery ground, the regulator ground, the engine-frame jumper.....


I have NO clue how this related to noise breaking the squelch....